JP2005164570A - Gas sensor and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor and its manufacturing method, by noting that a sol solution has liquidity at a normal temperature and solidity by baking at a predetermined temperature, utilizing the sol solution as a material for forming an adhesion layer, and finely ensuring the adhesion between the adhesion layer and a thick-film gas sensing layer. <P>SOLUTION: The sol solution becomes left and right adhesion layers 70, is applied in laminar manner to surface regions, corresponding to heating resistors 30 on a surface of a protective layer 50 by spin-coating method, and forms left-side and right-side sol solution layers. Pastes become a gas-sensing layer 80, and a reference layer 90, are printed on surfaces of the left-side and right-side sol solution layers by a screen printing method, and form the left and right paste layers. The sol solution layers and the paste layers are baked, and the adhesive layer, the gas-sensing layer and the reference layer are formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a gas sensor and a manufacturing method thereof.

  Conventionally, many gas sensors of this type have been proposed in which a plurality of thin films are stacked on a silicon substrate. As an example, there is a thermal sensor disclosed in Patent Document 1 below.

  This sensor has a hafnium oxide layer, and this hafnium oxide layer is formed as a thin film between an insulating film made of a silicon oxide film and a silicon nitride film formed on a silicon substrate and a heating resistor. Has been.

  Here, the insulating film constitutes a partition wall portion at a portion corresponding to the cavity portion formed on the silicon substrate from the back surface side. The heating resistor is formed as a thin film at a portion corresponding to the partition wall of the insulating film in the hafnium oxide layer.

Under such a configuration, the hafnium oxide layer relaxes the difference in thermal expansion between the heating resistor as a heat source and the insulating film, and maintains the adhesion between the heating resistor and the insulating film. Serves as an adhesion layer.
JP 2001-91486 A

  By the way, in the thermal type sensor as described above, a contact area can be increased between flat thin films such as a hafnium oxide layer and a heating resistor, and an adhesion layer made of a thin film such as a hafnium oxide layer is effective. It is thought that there is.

  However, between a flat thin film such as a hafnium oxide layer and a thick film formed of paste, since the thick film is composed of particulate components, point contact occurs between the thin film and the thick film, reducing the contact area. A large amount cannot be taken, and an adhesion layer made of a thin film is not effective.

  Therefore, for example, even if there is a request to apply the above-described hafnium oxide layer between the gas sensitive film and the heating resistor in the thermal sensor, the gas sensitive film is a thick film. However, the adhesion between the heat generating resistor and the gas sensitive film cannot be effectively ensured, and there arises a problem that the gas sensitive film and the heat generating resistor are likely to be peeled off.

  Therefore, in order to deal with the above, the present invention pays attention to the fact that the sol solution is liquid at room temperature and solidified by firing at a predetermined temperature. An object of the present invention is to provide a gas sensor that is employed as a forming material and that ensures good adhesion between the adhesion layer and the thick gas sensing layer, and a method for manufacturing the same.

  In solving the above-described problems, according to the gas sensor according to the present invention, a porous gas detection layer (80) formed in a thick film shape on a substrate (10, 20, 30, 50) is provided. Have

The gas sensor includes an insulating adhesion layer (70) formed between the gas detection layer and the substrate,
This adhesion layer is formed so as to be buried in the vicinity of the adhesion layer in the gas detection layer.

  Thus, since the adhesion layer is formed so as to be buried in the vicinity of the adhesion layer of the gas detection layer, the contact area between the adhesion layer and the area of the gas detection layer near the adhesion layer is small. Enlarge in 3D direction. Therefore, a good bond between the adhesion layer and the gas detection layer is ensured, and as a result, good adhesion between the gas detection layer and the substrate through the adhesion layer can be maintained.

According to the description of claim 2, the gas sensor according to the present invention is
A semiconductor substrate (10) formed by forming a cavity (11) in the plate thickness direction;
An insulating layer (20) formed on the semiconductor substrate and having a partition wall (21) at a portion corresponding to the cavity,
A heating resistor (30) formed on the partition;
A protective layer (50) formed on the insulating layer so as to cover the heating resistor;
A porous gas detection layer (80) formed in a thick film shape on the protective layer so as to face the heating resistor through this protective layer.

The gas sensor includes an insulating adhesive layer (70) formed between the gas detection layer and the protective layer so as to face the heating resistor through the protective layer,
This adhesion layer is formed so as to be buried in the vicinity of the adhesion layer in the gas detection layer.

  In the gas sensor using the semiconductor substrate having the cavity as described above, the adhesion layer is formed so as to be buried in the vicinity of the adhesion layer in the gas detection layer. The same effects as the invention can be achieved.

According to the description of claim 3, the gas sensor according to the present invention is
A sol solution layer (71) is formed on the substrate (10, 20, 30, 50) with a sol solution to be the insulating adhesive layer (70),
A paste layer (81) is formed on the sol solution layer with a paste to be a gas detection layer (80),
The sol solution layer and the paste layer are both fired to form an adhesion layer and a gas detection layer.

  In this way, a paste layer was formed on the sol solution layer, and the sol solution layer and the paste layer were both fired to form an adhesion layer and a gas detection layer. Here, when the paste layer is formed on the sol solution layer as described above, since the sol solution layer is in a liquid state, the sol solution layer is three-dimensionally mixed with the vicinity of the sol solution layer in the paste layer. .

  Therefore, the sol solution layer and the gas detection layer are baked together in the state of being mixed three-dimensionally as described above, and formed as an adhesion layer and a gas detection layer. For this reason, the contact area between the adhesion layer and the vicinity of the adhesion layer in the gas detection layer is expanded in the three-dimensional direction.

  As a result, good bonding between the adhesion layer and the gas detection layer is ensured, and as a result, good adhesion between the gas detection layer and the substrate through the adhesion layer can be maintained.

Moreover, according to the description of claim 4, the manufacturing method of the gas sensor according to the present invention,
A sol solution layer forming step of forming a sol solution layer (71) on a substrate (10, 20, 30, 50) with a sol solution to be an insulating adhesion layer (70);
After this sol solution layer forming step, a paste layer forming step of forming a paste layer (81) on the sol solution layer with a paste that becomes the gas detection layer (80);
After the paste layer forming step, there is provided a firing step in which the sol solution layer and the paste layer are fired together under a predetermined firing condition to form an adhesion layer and a gas detection layer.

  In this way, the sol solution layer is formed on the substrate with the sol solution that becomes the adhesion layer, and then the paste layer is formed on the sol solution layer with the paste that becomes the gas detection layer, and then the sol solution layer The paste layer was fired together under predetermined firing conditions to form an adhesion layer and a gas detection layer.

  Here, when the paste layer is formed on the sol solution layer as described above, the sol solution layer is three-dimensionally mixed with the vicinity of the sol solution layer in the paste layer. Therefore, the sol solution layer and the gas detection layer are baked together in the state of being mixed three-dimensionally as described above, and formed as an adhesion layer and a gas detection layer. For this reason, the contact area between the adhesion layer and the vicinity of the adhesion layer in the gas detection layer is expanded in the three-dimensional direction.

  As a result, a good bond between the adhesion layer and the gas detection layer is ensured, and as a result, it is possible to manufacture a gas sensor that can maintain good adhesion between the gas detection layer and the substrate via the adhesion layer.

Further, in the present invention, according to the description of claim 5, in the gas sensor manufacturing method according to claim 4, a dropping step of dropping the sol solution onto the gas detection layer after the firing step;
A refiring step of refiring the gas detection layer together with the adhesion layer under predetermined refiring conditions after the dropping step is characterized.

  Thus, after the firing step according to claim 4, the sol solution is dropped onto the gas detection layer, and then the gas detection layer is refired together with the adhesion layer under predetermined refiring conditions.

  Along with this, the sol solution spreads between the gas detection layer and the adhesion layer, so that it is possible to achieve the operational effect of the invention according to claim 4, and the gas detection layer and the adhesion layer. The degree of coupling between can be further improved. In other words, by spreading the sol, which is the same material as the material for forming the adhesion layer, over both the gas detection layer and the adhesion layer, the adhesion force between the gas detection layer and the adhesion layer is increased. It can be further improved.

  In the first, third, fourth, or fifth aspect, the substrate may have the following configuration.

  That is, the base is formed by forming a heating resistor on the semiconductor substrate or on the semiconductor substrate via an insulating layer, and forming a protective layer on the semiconductor substrate or the insulating layer so as to cover the heating resistor. Alternatively, a configuration in which a heating resistor is formed on a ceramic substrate such as alumina and a protective layer is formed on the ceramic substrate so as to cover the heating resistor may be employed.

  Moreover, in any one of Claims 1-5, if the formation material of an adhesion layer is the same formation material as a gas detection layer, the identity of each thermal expansion coefficient of an adhesion layer and a gas detection layer is securable. . Therefore, the adhesion between the adhesion layer and the gas detection layer in the invention according to any one of claims 1 to 5 can be further improved.

  Moreover, in any one of Claims 1-5, if the forming material of the contact | adherence layer is made into the insulating ceramic of a single component, the said contact | adherence layer does not contain the component used as a poisoning species with respect to a gas detection layer. Therefore, the adhesion layer does not cause poisoning of the gas detection layer.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

Hereinafter, each embodiment of the present invention will be described with reference to the drawings.
(First embodiment)
1 and 2 show a first embodiment of a catalytic combustion type gas sensor which is one of the gas sensors according to the present invention, and this catalytic combustion type gas sensor has a silicon semiconductor substrate 10 as shown in FIG. And both upper and lower insulating layers 20. The upper insulating layer 20 is formed on the surface of the semiconductor substrate 10, while the lower insulating layer 20 is formed on the back surface of the semiconductor substrate 10.

  Here, the left and right side cavities 11 shown in FIG. 1 are formed in the semiconductor substrate 10 at intervals on the back side of the upper insulating layer 20. Further, the lower insulating layer 20 is removed at portions corresponding to the cavities 11 to form openings of the cavities 11.

  Thus, the upper insulating layer 20 is exposed to the outside through the opening of each cavity 11 at each corresponding portion 21 (hereinafter also referred to as a partition wall 21) corresponding to each cavity 11. The semiconductor substrate 10 constitutes the substrate portion 12 at a portion other than each cavity portion 11.

  Further, as shown in FIG. 1, the gas sensor includes left and right heat generating resistors 30 and left, center and right wiring films 40. The left heating resistor 30 is formed in a zigzag shape on the left partition wall 21 of the upper insulating layer 20, while the right heating resistor 30 is formed in a zigzag pattern on the right partition wall 21 of the upper insulating layer 20. Has been.

  As shown in FIG. 1, the left wiring film 40 is located on the left side portion of the surface of the upper insulating layer 20 so as to correspond to the substrate portion 12 of the semiconductor substrate 10. As shown by 2, it is formed so as to be integrated with one end of the left heating resistor 30.

  As shown in FIG. 1, the central wiring film 40 is located on the central portion of the surface of the upper insulating layer 20 so as to correspond to the substrate portion 12 of the semiconductor substrate 10. 2 is formed so as to be integrated with the other end of the left heating resistor 30 and one end of the right heating resistor 30 as shown in FIG.

  Further, as shown in FIG. 1, the right wiring film 40 is located on the right side portion of the surface of the upper insulating layer 20 so as to correspond to the substrate portion 12 of the semiconductor substrate 10. 2 is formed so as to be integrated with the other end of the right heating resistor 30 as shown in FIG.

  Further, as shown in FIGS. 1 and 2, the gas sensor includes a protective layer 50 and left, center, and right electrode films 60, and the protective layer 50 covers each heating resistor 30. Thus, it is formed on the surface of the upper insulating layer 20. Here, in the protective layer 50, the contact holes 51 on the left side, the center side, and the right side are formed in portions corresponding to the wiring films 40 on the left side, the center side, and the right side of the protective layer 50. As a result, the left, center and right wiring films 40 are exposed outwardly through the left, center and right contact holes 51 on the surface.

  The left, center and right electrode films 60 are formed on the left, center and right wiring films 40 through the left, center and right contact holes 51.

  As shown in FIG. 1, the gas sensor also includes a left and right contact layer 70, a porous gas detection layer 80, and a reference layer 90. The left adhesion layer 70 is formed in a layered form on the protective layer 50 corresponding to the left heating resistor 30, and the left adhesion layer 70 corresponds to the left heating resistor 30 corresponding to the left heating resistor 30 and the gas. It plays a role of improving adhesion between the sensing layer 80 and the sensor layer 80.

  On the other hand, the right adhesion layer 70 is formed in a layered form on the protective layer 50 corresponding to the right heating resistor 30, and the right adhesion layer 70 corresponds to the right heating resistor 30 in the protective layer 50. And the reference layer 90 to improve adhesion.

  The gas detection layer 80 is formed on the left adhesion layer 70 in a laminated form, while the reference layer 90 is formed on the right adhesion layer 70 in a laminated form.

  In the present embodiment, the gas detection layer 80, the left adhesion layer 70, and the left heating resistor 30 constitute a gas detection unit in the catalytic combustion gas sensor. Further, the reference layer 90, the right adhesion layer 70, and the right heating resistor 30 constitute a temperature compensation unit in the catalytic combustion gas sensor. The temperature compensation unit has the same heat capacity as that of the gas detection unit, and is made of a material that is inert to the gas.

Next, the manufacturing process of the gas sensor configured as described above will be described with reference to FIGS.
(1) Formation process of each insulating layer 20 A silicon substrate is prepared as the semiconductor substrate 10 (see FIG. 3). The reason why the silicon substrate is employed as the semiconductor substrate 10 in this way is that the silicon substrate can be easily reduced in size by a fine processing technique.

After cleaning the semiconductor substrate 10 thus prepared, silicon oxide films (SiO ₂ films) are formed on the front and back surfaces of the semiconductor substrate 10 by, for example, thermal oxidation. Next, a silicon nitride film (Si ₃ N ₄ film) and a silicon oxide film are sequentially formed in a laminated form on the silicon oxide film formed on the surface of the semiconductor substrate 10 by chemical vapor deposition. On the other hand, a silicon nitride film (Si ₃ N ₄ film) is formed in a laminated manner on the silicon oxide film formed on the back surface of the semiconductor substrate 10 by chemical vapor deposition.

As a result, the silicon oxide film, the silicon nitride film, and the silicon oxide film formed on the surface of the semiconductor substrate 10 as described above are formed as the upper insulating layer 20 with a three-layer structure. A silicon oxide film and a silicon nitride film formed in a stacked manner as described above are formed on the back surface as the lower insulating layer 20 with a two-layer structure (see FIG. 4). Each insulating layer 20 is formed to a thickness within the range of 50 (nm) to 2000 (nm), for example, within a range of 100 (nm) to 1000 (nm). With such a thickness, it is possible to satisfactorily ensure the electrical insulation characteristics as the insulating layer 20.
(2) Step of forming each heating resistor 30 and each wiring film 40 After each insulating layer 20 is formed as described above, the lower tantalum film (Ta film) is formed on the upper insulating layer 20 in an atmosphere at a predetermined temperature. The surface is formed by sputtering, and then a platinum film (Pt film) is formed on the lower tantalum film by sputtering, and the upper tantalum film is formed on the platinum film by sputtering. The lower tantalum film has a role of increasing the adhesion strength between the platinum film and the upper insulating layer 20.

Thereafter, portions of the upper tantalum film, the platinum film, and the lower tantalum film other than the corresponding portions corresponding to the heating resistors 30 and the wiring films 40 are removed by photolithography. As a result, the left and right heating resistors 30 and the left, center and right wiring films 40 are formed on the surface of the upper insulating layer 20 as shown in FIG.
(3) Step of forming protective layer 50 After forming each heating resistor 30 and each wiring film 40 as described above, a silicon oxide layer (SiO ₂ layer) is formed by chemical vapor deposition using each heating resistor 30 and each wiring film 40. A film is formed on the surface of the upper insulating layer 20 so as to cover the wiring film 40. Further, on the silicon oxide layer, a silicon nitride layer (Si ₃ N ₄ layer) is formed in a laminated form by a chemical vapor deposition method.

  Next, each portion corresponding to each wiring film 40 in the stacked layer of the silicon nitride layer and the silicon oxide layer is removed by etching under a photolithography process. Thereby, the protective layer 50 having the contact holes 51 on the left side, the center side, and the right side is formed on the surface of the upper insulating layer 20 so as to cover each heating resistor 30 as shown in FIGS. Is done.

The protective layer 50 is formed to a thickness within the range of 50 (nm) to 2000 (nm), for example, within a range of 100 (nm) to 1000 (nm), as with each insulating layer 20. To do. With such a thickness, good electrical insulation characteristics as the protective layer 50 can be secured. Further, each wiring film 40 is exposed to the outside through the corresponding contact hole 51.
(4) Step of forming each electrode film 60 After forming the protective layer 50 as described above, a conductive metal such as platinum (Pt), gold (Au), aluminum (Al), or nickel (Ni) is chemically deposited. It forms as a metal film on the protective layer 50 by general film-forming methods, such as a method or a physical vapor deposition method. Thereafter, portions of the metal film formed in this way other than the corresponding portions with respect to the contact holes 51 are removed by etching under a photolithography process.

As a result, the left, center, and right electrode films 60 are formed corresponding to the contact holes 51 as shown in FIG. Note that the thickness of each electrode 60 is desirably within a range of 100 (nm) to 2000 (nm), for example, within a range of 400 (nm) to 1200 (nm).
(5) Formation Step of Each Cavity 11 After each electrode film 60 is formed as described above, each part corresponding to the left and right heating resistors 30 in the lower insulating layer 20 is subjected to photolithography processing. The portions of the semiconductor substrate 10 corresponding to the removed portions are removed by anisotropic etching using an aqueous tetramethylammonium hydroxide solution, and the heating resistors 30 in the upper insulating layer 20 are removed. The corresponding part is exposed to the outside.

As a result, the left and right side cavities 11 are formed in portions of the semiconductor substrate 10 and the lower insulating layer 20 corresponding to the respective heating resistors 30 as shown in FIG.
(6) Formation process of each adhesion layer 70 and gas detection layer 80, and reference layer 90 After each cavity part 11 is formed as mentioned above, each adhesion layer 70, gas detection layer 80, and reference layer 90 are formed as follows. Together.

  A sol solution to be the left and right adhesion layers 70 is applied in a layer form by spin coating on the surface of the protective layer 50 corresponding to each heating resistor 30 to form the left and right sol solution layers 71. (See FIG. 10). In order to prevent the sol solution from being applied to a portion of the surface of the protective layer 50 other than the corresponding surface portion for each heating resistor 30, when applying the sol solution, the corresponding to each heating resistor 30. A masking process such as a tape is applied to a part other than the surface part to prevent the sol solution from being applied.

  Next, each paste to be the gas detection layer 80 and the reference layer 90 is printed on the surface of each of the left and right sol solution layers 71 by screen printing to form a left paste layer 81 and a right paste layer 91 (FIG. 11). reference). Since the sol solution layer is formed by spin coating, the sol solution layer can be formed easily and inexpensively.

  Here, it is desirable to apply the paste to be the gas detection layer 80 to a thickness such that the thickness of the gas detection layer 80 is 5 (μm) or more and 500 (μm) or less. The reason why the thickness of the gas detection layer 80 is set to 5 (μm) or more is to configure the gas detection layer 80 as a so-called thick film. The reason why the thickness of the gas detection layer 80 is 500 (μm) or less is to suppress an extreme increase in the heat capacity of the gas detection layer. In the present embodiment, the thickness of each of the paste layers 81 and 91 is, for example, 50 (μm). Moreover, the thickness of each sol solution layer 71 mentioned above was 1.0 (micrometer), for example.

  Further, as the sol solution to be each adhesion layer 70, a solution made of alumina sol is employed. In this embodiment, as the solution, colloidal particles of alumina hydrate having a particle size within a range of 10 (nm) to 20 (nm) are dispersed in water by about 20 (%), and a range of 3 to 5 is obtained. A solution made of an alumina sol having a pH within a range and a viscosity within a range of 1 (mPa · s) to 25 (mPa · s) (viscosity at 25 (° C.)) is employed.

On the other hand, examples of the paste that becomes the gas detection layer 80 include porous ceramics such as alumina (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), and titanium oxide (TiO ₂ ), platinum (Pt), and palladium (Pd). , Ruthenium (Ru) or rhodium (Rh) or a noble metal species such as an alloy thereof is supported as a powder catalyst, and a paste prepared by mixing an appropriate amount of a binder or a solvent with the powder catalyst is employed. Moreover, the paste used as the reference layer 90 employs a material inert to the gas.

  However, from the viewpoint of securing the same coefficient of thermal expansion between the gas detection layer 80 and the reference layer 90 of each adhesion layer 70, the sol solution mainly includes the same material as the paste serving as the gas detection layer. It is desirable. For example, when the paste serving as the gas detection layer is based on alumina, the sol solution is preferably an alumina sol. In the present embodiment, alumina is used as a component for both the paste and the sol solution serving as the gas detection layer.

  When the paste layers 81 and 91 are formed on the surface of each sol solution layer 71 as described above, the left sol solution layer 71 is in a liquid state together with the left paste layer 81, so that it is not in contact with the paste layer 81. Thus, the paste layer 81 is three-dimensionally mixed with each other and reaches the entire lower portion of the paste layer 81. In such a process, since the sol component of the left sol solution layer 71 is in a liquid state, the left sol solution layer 71 is mixed with the entire lower portion of the paste layer 81 so as to be mixed three-dimensionally with each other. It will be buried. Accordingly, the left sol solution layer 71 becomes a mixed layer with the lower portion of the left paste layer 81.

  On the other hand, since the right sol solution layer 71 is in a liquid state together with the right paste layer 91, the paste layer 91 is mixed three-dimensionally with the paste layer 91 at the contact point with the paste layer 91. Go to the whole of the lower part of. In such a process, since the sol component of the right sol solution layer 71 is in a liquid state, the right sol solution layer 71 is mixed with the entire lower portion of the right paste layer 91 in a three-dimensional manner. It will be buried in. Accordingly, the right sol solution layer 71 becomes a mixed layer with the lower portion of the right paste layer 91.

  The structure (see FIG. 11) in such a state is fired under predetermined firing conditions. As a result, the paste layers 81 and 91 and the sol solution layers 71 are simultaneously fired under the predetermined firing conditions.

  In the process of co-firing, as described above, the sol solution layer 71 that becomes the left adhesion layer 70 is fired and solidified while being mixed with the entire lower portion of the paste layer 81 that becomes the gas detection layer 80. As described above, the sol solution layer 71 that becomes the right adhesion layer 70 is baked and solidified in a state of being mixed with the entire lower portion of the paste layer 91 that becomes the reference layer 90.

  In other words, in the co-firing process as described above, both the left sol solution layer 71 and the left paste layer 81 are solidified to form the left adhesion layer 70 and the gas detection layer 80, and the right sol solution layer 71 and the right paste Both layers 91 are solidified to form the left adhesion layer 70 and the reference layer 90 (see FIG. 1).

  In such a formation state, the left adhesion layer 70 extends so as to be buried in the entire lower portion of the gas detection layer 80. For this reason, the contact area with the left adhesion layer 70 of the gas detection layer 80 expands in the three-dimensional direction. Therefore, the left adhesion layer 70 is chemically bonded to the entire lower portion of the gas detection layer 80 in a three-dimensional contact with no gap in a wide range.

  As a result, it is possible to ensure excellent adhesion between the gas detection layer 80 and the left adhesion layer 70, and to prevent the gas detection layer 80 from peeling from the left heating resistor 30 in advance. Further, in the contact combustion type gas sensor, as the contact area of the gas detection layer 80 with the left adhesion layer 70 is increased as described above, heat transfer from the gas detection layer 80 to the left heating resistor 30 is improved. .

  Further, in the formation state as described above, the right adhesion layer 70 extends so as to be buried in the entire lower portion of the reference layer 90. For this reason, the contact area of the reference layer 90 with the right contact layer 70 is expanded in the three-dimensional direction. Accordingly, the right adhesion layer 70 is chemically bonded to the entire lower portion of the reference layer 90 in a three-dimensional contact with no gap in a wide range. As a result, excellent adhesion between the reference layer 90 and the right adhesion layer 70 can be ensured, and peeling of the reference layer 90 from the right heating resistor 30 can be prevented in advance.

  The sol component of the sol solution layer that becomes the adhesion layer 70 is alumina as described above, and is the same as the component of the base of the paste layer that becomes the gas detection layer 80 and the reference layer 90. Accordingly, since the left adhesion layer 70 and the gas detection layer 80 have substantially the same thermal expansion coefficient, the adhesion between the gas detection layer 80 and the left adhesion layer 70 described above is further improved. This is the same between the right adhesion layer 70 and the reference layer 90.

  Here, since the gas detection layer 80 and the left adhesion layer 70 are formed by simultaneous firing as described above, only one firing is required. Therefore, the formation of the gas detection layer 80 and the left adhesion layer 70 is simple and helps to save the electricity bill of the firing furnace for firing.

  Further, since the sol component of the sol solution layer 71 is single-component alumina and does not contain poisonous substances, the adhesion layer 70 does not become a poisoned species. Therefore, the adhesion layer 70 does not cause deterioration of the gas detection layer 80.

  Moreover, since the sol solution layer 71 baked once does not flow again, the adhesion layer 70 can stably maintain the adhesion to the gas detection layer and the reference layer.

  Further, the thickness of each adhesion layer 70 is not particularly limited, but has a thickness of at least 1% of the thickness of the gas detection layer 80 and the reference layer 90 in order to ensure the above-described adhesion. It is desirable. In addition, if the contact area of the left adhesion layer 70 with the gas detection layer 80 is too large, the sensitivity of the gas detection layer 80 to the gas is reduced. Therefore, the thickness of the left adhesion layer 70 is equal to the thickness of the gas detection layer 80. 10 (%) or less is desirable. Note that the thickness of the right adhesion layer 70 is desirably 10% or less of the thickness of the reference layer 90.

  Therefore, it is desirable to form each sol solution layer 71 so as to satisfy such a thickness. The catalytic combustion type gas sensor is manufactured through the above steps.

  The heating resistor 30 of the temperature compensation unit is desirably formed so as not to be affected by a change in resistance value of the heating resistor 30 of the gas detection unit. Since the heating resistor 30 of the temperature compensation unit is used in combination with the heating resistor 30 of the gas detection unit, it is desirable that the resistance values of both the heating resistors are substantially the same.

  Moreover, since the gas detection unit and the temperature compensation unit are provided on the same semiconductor substrate as described above, it is desirable that the gas detection unit and the temperature compensation unit are not affected by heat from each other.

  Incidentally, when the gas detection layer 80 and the left adhesion layer 70 in the gas sensor of the present embodiment were photographed with a scanning electron microscope together with the protective layer 50, a photograph as shown in FIG. 12 was obtained. This shows that the contact state between the lower part of the gas detection layer 80 and the left adhesion layer 70 is three-dimensional.

  Moreover, the peel test of the gas sensor in this embodiment was performed in comparison with the comparative example. However, the comparative example is a gas sensor in which the gas detection layer 80 and the reference layer 90 are directly formed on the protective layer 50 by eliminating the adhesion layer in the gas sensor of the present embodiment.

  Thus, in the above comparative example, an adhesive tape (T-112 type mending tape manufactured by KOKUYO Co., Ltd.) was applied to the surface of the gas detection layer 80, and then the adhesive tape was peeled off. (See FIG. 13). In FIG. 13, a substantially elliptical region drawn on the surface of the protective layer 50 shows a trace of the gas detection layer 80 peeling off.

  On the other hand, when a pressure-sensitive adhesive tape was applied to the surface of the gas detection layer 80 in the gas sensor of the present embodiment and then the pressure-sensitive adhesive tape was peeled off, the gas detection layer 80 did not peel (see FIG. 14). This also shows that the adhesion layer 70 can maintain the adhesion between the gas detection layer 80 and the protective layer 50 in the gas sensor of the present embodiment.

Further, even when the heating resistor of the gas sensor manufactured in this embodiment was intermittently energized by pulse driving, the gas detection layer 80 did not peel off. Furthermore, although the test which drops the said gas sensor from the height of 1 (m) on a floor was done, the gas detection layer 80 did not peel. Therefore, even if an external impact is applied to the gas sensor during transportation of the gas sensor, the gas detection layer 80 does not peel off.
(Second Embodiment)
FIG. 15 shows a second embodiment of the present invention. In the second embodiment, in the gas sensor described in the first embodiment, the lower insulating layer 20 and the reference layer 90 are eliminated, and the semiconductor substrate 10 has a shape in which each cavity 11 is eliminated. Other configurations are the same as those in the first embodiment.

  In the second embodiment configured as described above, in manufacturing the gas sensor, the process of forming the lower insulating layer 20 described in the first embodiment and the formation of each cavity 11 of the semiconductor substrate 10 are performed. Although the process and the process of forming the reference layer 90 are abolished, other processes are performed in the same manner as in the first embodiment. Thereby, the gas sensor which has the cross-sectional shape shown in FIG. 15 is manufactured.

  In this manufacturing process, the gas detection layer 80 is formed on the left adhesion layer 70 under the same simultaneous firing as described in the first embodiment (see FIGS. 10 and 11).

Accordingly, as described in the first embodiment, excellent adhesion can be ensured between the gas detection layer 80 and the left adhesion layer 70, and as a result, the same as in the first embodiment. The effect of this can be achieved.
(Third embodiment)
Next, a third embodiment of the present invention will be described. The third embodiment is different from the gas sensor manufacturing process described in the first embodiment in that it is a manufacturing process in which the following processes are added. Other configurations are the same as those in the first embodiment.

  That is, in the third embodiment, as described in the first embodiment, in the manufacturing process, the structure shown in FIG. 11 is finally fired under the predetermined firing conditions. The two sol solution layers 71 to be the right and left side adhesion layers 70, the paste layer 81 to be the gas detection layer 80, and the paste layer 91 to be the reference layer 90 are simultaneously fired. Thereby, as described in the first embodiment, the left and right side adhesion layers 70, the gas detection layer 80, and the reference layer 90 (see FIG. 1) are formed.

  Thereafter, in the third embodiment, a diluted solution obtained by diluting the alumina sol solution 10 times with pure water is dropped onto both the gas detection layer 80 and the reference layer 90 (see FIG. 1) from each upper part thereof. . Here, the dropping is performed twice with such an amount that the diluted solution penetrates both the gas detection layer 80 and the reference layer 90 as a whole.

  After dropping the diluted solution in this way, the gas sensor of FIG. 1 is additionally baked under predetermined re-baking conditions (for example, baking temperature 700 (° C.) and baking time 1 (hour)). As a result, the gas detection layer 80 and the reference layer 90 infiltrated with the diluted solution as described above are co-fired under the re-baking conditions.

  Along with this, the alumina sol solution spreads between the gas detection layer 80 and the left adhesion layer 70 and between the reference layer 90 and the right adhesion layer 70. Therefore, the degree of coupling between the gas detection layer 80 and the left adhesion layer 70 and the degree of coupling between the reference layer 90 and the right adhesion layer 70 are more than those in the case of the gas sensor described in the first embodiment. Further improve.

  In other words, the alumina sol, which is the same material as the material for forming the adhesion layer 70, is spread over both the gas detection layer 80 and the left adhesion layer 70 and both the reference layer 90 and the right adhesion layer 70. Thus, the adhesion force between the gas detection layer 80 and the left adhesion layer 70 and the adhesion force between the reference layer 90 and the right adhesion layer 70 are more than those of the gas sensor described in the first embodiment. Can be further improved.

  Thereby, at the stage finally fired in the manufacturing process described in the first embodiment, even if the gas detection layer and the reference layer are aggregated and there is partial peeling at the interface with the adhesion layer, Such partial peeling can be prevented in advance by adopting the additional process described in the third embodiment. In addition, by making the dripping amount of the diluted solution an appropriate amount, the adhesion force between the gas detection layer 80 and the left adhesion layer 70 and the reference layer 90 described above can be obtained without deteriorating the gas detection characteristics as a gas sensor. Only the adhesion force between the right adhesion layer 70 and the right adhesion layer 70 can be improved.

  Incidentally, when the gas detection layer 80 and the left adhesion layer 70 in the gas sensor of the third embodiment were photographed together with the protective layer 50 with a scanning electron microscope, a photograph as shown in FIG. 16 was obtained. According to this, the alumina sol spreads between the gas detection layer 80 and the left adhesion layer 70 by dropping the diluted solution as described above, and the degree of bonding between the gas detection layer 80 and the left adhesion layer 70. It can be seen that is further improved.

  In addition, a peel test of the gas sensor in the third embodiment was performed. This peeling test was performed by dropping water droplets onto the gas sensor to such an extent that the gas detection layer 80 of the gas sensor was buried in the water droplet and heating the gas sensor at 400 (° C.). The peel test was also applied as a comparative example to the gas sensor described in the first embodiment.

According to this, although there is a gas sensor that does not drop the alumina sol solution as described in the third embodiment (gas sensor of the first embodiment), peeling occurs, but the gas sensor of the third embodiment. Then, even if the said peeling test was done 10 times, neither peeling nor damage generate | occur | produced. Therefore, it can be seen that the adhesion strength between the gas detection layer and the adhesion layer in the gas sensor of the third embodiment is further improved as compared with the gas sensor of the first embodiment.
(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, similarly to the second embodiment, the lower insulating layer 20 and the reference layer 90 are eliminated in the gas sensor described in the first embodiment, and the semiconductor substrate 10 is formed in each cavity 11. The shape is abolished. In manufacturing the gas sensor having such a shape, the manufacturing process described in the third embodiment is employed in the fourth embodiment.

  That is, in the fourth embodiment, in manufacturing the gas sensor, the process of forming the lower insulating layer 20 described in the first embodiment, the process of forming each cavity 11 of the semiconductor substrate 10, and the reference layer The process of forming 90 is abolished, but the other steps are the same as in the third embodiment.

  Therefore, in the fourth embodiment, after the same co-firing as in the first embodiment, the diluted solution penetrates the entire gas detection layer 80 in the same manner as described in the third embodiment. Drip twice with the amount. Thereafter, the gas sensor of FIG. 15 is additionally baked under the re-baking conditions described in the third embodiment. Thereby, the gas detection layer 80 infiltrated with the diluted solution as described above is fired under the re-baking conditions. As a result, the same effects as those in the third embodiment can be achieved with respect to the degree of bonding and adhesion between the gas detection layer 80 and the left adhesion layer.

In carrying out the present invention, the following various modifications are possible without being limited to the above embodiments.
(1) Each insulating layer 20 or protective layer 50 is not limited to a multiple layer as described in the above embodiments, but is a silicon oxide film (SiO ₂ film) or a silicon nitride film (Si ₃ N ₄ film). Therefore, it may be formed in a single layer.

Note that a tantalum oxide film (Ta ₂ O ₅ film) or alumina (Al ₂ O ₃ film) may be employed instead of the silicon nitride film. Note that the thin film forming method of the insulating layer 20 is not limited to the chemical vapor deposition method, and may be, for example, a physical vapor deposition method or a spin coating method.
(2) Each insulating layer 20 may be formed as follows. That is, after cleaning the semiconductor substrate 10, silicon oxide films (SiO ₂ films) are formed on the front and back surfaces of the semiconductor substrate 10 by a thin film forming method (for example, chemical vapor deposition).

Next, silicon nitride films (Si ₃ N ₄ films) on both the upper and lower sides are formed on the silicon oxide films on the upper and lower sides of the semiconductor substrate 10 by chemical vapor deposition. Thus, the upper silicon oxide film and the upper silicon nitride film of the semiconductor substrate 10 are formed as the upper insulating layer 20, while the lower silicon oxide film and the lower silicon nitride film of the semiconductor substrate 10 are formed as the lower insulating layer 20. To do.
(3) The heating resistor 30 only needs to heat the partition wall 21 and the gas detection layer 80 of the upper insulating layer 20 to a predetermined temperature. Therefore, the heating resistor 30 may be a film made of gold (Au) or ruthenium (Ru) instead of the platinum film, and may generally be a noble metal. The heating resistor 30 may be made of silicon (Si).

Note that the tantalum film described in the process of forming the heating resistor may be eliminated if necessary. Further, the temperature coefficient of resistance of the heating resistor 30 may be either positive or negative.
(4) The formation of the sol solution to be the adhesion layer 70 as the sol solution layer is not limited to the spin coating method, and may depend on a screen printing method or a coating method. Also by this, the sol solution layer can be easily formed as in the case of the spin coating method, and the cost can be reduced.
(5) The paste used as the gas detection layer 80 is a paste made of only the above porous ceramics, and the paste thus formed is platinum (Pt), palladium (Pd), ruthenium (Ru) or rhodium (Rh). It may be formed by immersing in a solution containing a noble metal such as and supporting the noble metal.
(6) In forming the paste to be the gas detection layer 80 as a paste layer, the paste is not limited to the screen printing method and may depend on dipping with a dispenser.
(7) Since the sol solution is formed as a sol solution layer as described above and remains in a liquid state, it is not baked alone, but the sol solution layer may be subjected to a heat treatment on the order of dehydration.

Even in this case, when the paste layer that becomes the gas detection layer or the reference layer is formed on the sol solution layer after the heat treatment, the sol solution layer absorbs moisture from the paste layer and becomes liquid again. This is to return to the liquid state before the dehydration process.
(8) Instead of the semiconductor substrate 10 and the upper insulating layer 20, an alumina substrate is employed, an adhesion layer is formed on the alumina substrate via a heating resistor, and a gas detection layer is formed on the adhesion layer. May be.
(9) The present invention is not limited to the catalytic combustion type gas sensor, and for example, the present invention may be applied to a semiconductor type gas sensor having a heating resistor and a gas detection layer corresponding to the heating resistor and the gas detection layer of the catalytic combustion type gas sensor. Good.

Here, as a paste which becomes a porous gas detection layer of the semiconductor gas sensor, an oxide semiconductor such as tin oxide (SnO ₂ ) or zinc oxide (ZnO) is used as a base, and platinum (Pt) or palladium is used as the base. A paste formed by supporting (Pd) or the like is employed.

  In addition, the paste may be a paste of a noble metal such as platinum (Pt), palladium (Pd), ruthenium (Ru), or rhodium (Rh) that is previously supported on an oxide semiconductor. Then, only the oxide semiconductor is pasted, and the paste thus obtained is immersed in a solution containing a powdered noble metal such as platinum (Pt), palladium (Pd), ruthenium (Ru) or rhodium (Rh). And may be formed by supporting the noble metal.

The semiconductor gas sensor detects the gas concentration by a change in electric resistance of the gas detection layer based on the gas adsorption phenomenon by the gas detection layer.
(10) In the gas sensor described in the first embodiment, the reference layer constituting the temperature compensation unit may be eliminated, and the temperature compensation unit may be a temperature compensation unit including only a heating resistor. The temperature compensation unit may be abolished.
(11) The sol solution to be the adhesion layer 70 described above is not limited to the solution made of alumina sol, but may be, for example, a solution made of silica sol or titania sol. Any solution made of a material may be used.

FIG. 3 is a sectional view taken along line 1-1 in FIG. 1 is a schematic plan view showing a first embodiment of a catalytic combustion gas sensor according to the present invention. It is sectional drawing of the semiconductor substrate of FIG. It is sectional drawing which shows the formation process of the upper-and-lower both-side insulating layer with respect to the semiconductor substrate of FIG. It is sectional drawing which shows the formation process of each wiring film with respect to the upper side insulating layer of FIG. 3, and each heating resistor. It is sectional drawing which shows the formation process of the protective layer with respect to the upper side insulating layer of FIG. It is sectional drawing which shows the formation process of each wiring film with respect to the protective layer of FIG. It is sectional drawing which shows the formation process of each electrode film with respect to the protective layer of FIG. FIG. 9 is a cross-sectional view showing a step of forming each cavity of the semiconductor substrate via the lower insulating layer of FIG. 8. It is sectional drawing which shows the formation process of each sol solution layer with respect to the protective layer of FIG. It is sectional drawing which shows the formation process of each paste layer with respect to each sol solution layer of FIG. It is the partial photography sectional view which photoed the gas detection layer in the 1st embodiment with the left adhesion layer and the protective layer. It is a partial top view after giving a peeling test to a comparative example. It is a partial top view after giving the peeling test to the gas sensor of the said 1st Embodiment. It is sectional drawing of 2nd Embodiment of this invention. It is the partial photography sectional view which photoed the gas detection layer in the above-mentioned 3rd embodiment with the left adhesion layer and the protective layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate, 11 ... Cavity part, 20 ... Insulating layer, 21 ... Partition part, 30 ... Heating resistor,
50 ... protective layer, 70 ... adhesion layer, 71 ... sol solution layer, 80 ... gas detection layer, 81 ... paste layer, 90 ... reference layer.

Claims (5)

In a gas sensor having a porous gas detection layer formed in a thick film shape on a substrate,
An insulating adhesion layer formed between the gas detection layer and the substrate;
The adhesion layer is formed so as to be buried in a portion of the gas detection layer near the adhesion layer. A semiconductor substrate formed with a cavity in the thickness direction;
An insulating layer formed on the semiconductor substrate and having a partition wall at a portion corresponding to the cavity;
A heating resistor formed on the partition;
A protective layer formed on the insulating layer so as to cover the heating resistor;
In the gas sensor having a porous gas detection layer formed in a thick film shape on the protective layer so as to face the heating resistor through the protective layer,
An insulating adhesive layer formed between the gas detection layer and the protective layer so as to face the heating resistor through the protective layer;
The adhesion layer is formed so as to be buried in a portion of the gas detection layer near the adhesion layer. A sol solution layer is formed on a substrate with a sol solution that becomes an insulating adhesive layer,
A paste layer is formed on the sol solution layer with a paste serving as a gas detection layer,
A gas sensor for firing the sol solution layer and the paste layer together to form the adhesion layer and the gas detection layer. A sol solution layer forming step of forming a sol solution layer on a substrate with a sol solution to be an insulating adhesive layer;
After this sol solution layer forming step, a paste layer forming step of forming a paste layer on the sol solution layer with a paste that becomes a gas detection layer;
A gas sensor manufacturing method comprising: a baking step of baking the sol solution layer and the paste layer together under a predetermined baking condition to form the adhesion layer and the gas detection layer after the paste layer forming step. A dropping step of dropping the sol solution onto the gas detection layer after the firing step;
The method for producing a gas sensor according to claim 4, further comprising a refiring step of refiring the gas detection layer together with the adhesion layer under predetermined refiring conditions after the dropping step.

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